Replaced permutation class with permutation function

Vector based permutations (permutation class) are easily modelled with
expression based permutations (used to be called vex::eslice()). This
commit drops permutation class and renames vex::eslice() to
vex::permutation(). See README and tests/vector_view.cpp for examples.

Author: ddemidov

README.md

@@ -315,26 +315,25 @@ a sequence position N.
 
 ### <a name="permutations"></a>Permutations
 
-`vex::permutation` allows to use permuted vector in a vector expression. The
-class constructor accepts `vex::vector<size_t>` of indices. The following
-example assigns reversed vector `X` to `Y`:
+`vex::permutation()` function allows to use permuted vector in a vector
+expression. The function accepts a vector expression that returns integral
+values (indices).  The following example assigns reversed vector `X` to `Y`:
 
 ~~~{.cpp}
 vex::vector<size_t> I(ctx, N);
 I = N - 1 - vex::element_index();
-
-vex::permutation reverse(I);
+auto reverse = vex::permutation(I)
 
 Y = reverse(X);
 ~~~
 
 The drawback of the above approach is that you have to store and access an
 index vector. Sometimes this is a necessary evil, but in this simple example we
-can do better. `vex::eslice()` function returns an expression-based permutation
-operator. Here is how we use it:
+can do better. In the following example lightweight expression is used to
+construct the same permutation:
 
 ~~~{.cpp}
-auto reverse = vex::eslice( N - 1 - vex::element_index() );
+auto reverse = vex::permutation( N - 1 - vex::element_index() );
 Y = reverse(X);
 ~~~
 

tests/vector_view.cpp

@@ -117,16 +117,16 @@ BOOST_AUTO_TEST_CASE(vector_permutation)
     {
         vex::vector<size_t> I(queue, N);
         I = N - 1 - vex::element_index();
-        vex::permutation reverse(I);
-        Y = reverse(X);
+        auto reverse = vex::permutation(I);
 
+        Y = reverse(X);
         check_sample(Y, [&](size_t idx, double v) { BOOST_CHECK_EQUAL(v, x[N - 1 - idx]); });
     }
 
     Y = 0;
 
     {
-        auto reverse = vex::eslice(N - 1 - vex::element_index());
+        auto reverse = vex::permutation(N - 1 - vex::element_index());
 
         Y = reverse(X);
         check_sample(Y, [&](size_t idx, double v) { BOOST_CHECK_EQUAL(v, x[N - 1 - idx]); });
@@ -192,7 +192,7 @@ BOOST_AUTO_TEST_CASE(assign_to_view) {
 
     I = vex::element_index() * m;
 
-    vex::permutation first_col(I);
+    auto first_col = vex::permutation(I);
 
     first_col(x) = 42;
 

vexcl/vector_view.hpp

@@ -507,64 +507,12 @@ struct slicer {
         }
 };
 
-/// Permutation operator.
-struct permutation {
-    const vector<size_t> &index;
-
-    permutation(const vector<size_t> &index) : index(index) {
-        assert(index.queue_list().size() == 1);
-    }
-
-    size_t size() const {
-        return index.size();
-    }
-
-    std::string partial_expression(const std::string &prm_name,
-            const cl::Device&) const
-    {
-        std::ostringstream s;
-        s << prm_name << "_base[" << prm_name << "_index[idx]]";
-
-        return s.str();
-    }
-
-    std::string indexing_function(const std::string &/*prm_name*/,
-            const cl::Device&) const
-    {
-        return "";
-    }
-
-    template <typename T>
-    std::string parameter_declaration(const std::string &prm_name,
-            const cl::Device&) const
-    {
-        std::ostringstream s;
-
-        s << ",\n\tglobal " << type_name<T>() << " * " << prm_name << "_base"
-          << ", global " << type_name<size_t>() << " * " << prm_name << "_index";
-
-        return s.str();
-    }
-
-    void setArgs(cl::Kernel &kernel, unsigned device, size_t/*index_offset*/,
-	    unsigned &position) const
-    {
-        kernel.setArg(position++, index(device));
-    }
-
-    template <typename T>
-    vector_view<T, permutation> operator()(const vector<T> &base) const {
-        assert(base.queue_list().size() == 1);
-        return vector_view<T, permutation>(base, *this);
-    }
-};
-
 /// Expression-based permutation operator.
 template <class Expr>
-struct expr_slice {
+struct expr_permutation {
     const Expr expr;
 
-    expr_slice(const Expr &expr) : expr(expr) {}
+    expr_permutation(const Expr &expr) : expr(expr) {}
 
     size_t size() const {
         detail::get_expression_properties prop;
@@ -618,9 +566,9 @@ struct expr_slice {
     }
 
     template <typename T>
-    vector_view<T, expr_slice> operator()(const vector<T> &base) const {
+    vector_view<T, expr_permutation> operator()(const vector<T> &base) const {
         assert(base.queue_list().size() == 1);
-        return vector_view<T, expr_slice>(base, *this);
+        return vector_view<T, expr_permutation>(base, *this);
     }
 };
 
@@ -635,10 +583,10 @@ struct expr_slice {
 template <class Expr>
 typename std::enable_if<
     std::is_integral<typename detail::return_type<Expr>::type>::value,
-    expr_slice<Expr>
+    expr_permutation<Expr>
 >::type
-eslice(const Expr &expr) {
-    return expr_slice<Expr>(expr);
+permutation(const Expr &expr) {
+    return expr_permutation<Expr>(expr);
 }
 
 //---------------------------------------------------------------------------